Loaded-telephone-line system



T. SHAW AND W. FONDILLER.

LOADED TELEPHONE LINE SYSTEM.

APPLICAT ON FILED JULY 16. 1918.

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THOMAS SHAW, OF HACKENSACK, NEW JERSEY, ANDWILLIAM FONDILLER, OF NEW YORK, N. Y., ASSIGNORSTO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

LOADED-TELEPHONE-LINE SYSTEM.

Original application filed September 12, 1914, Serial No. 861,421. Patent No. 1,289,941.

Divided and this application filed July 16, 1918. Serial No. 245,138.

To all w/zom 2'2- may concern:

Be it known that we, THOMAS SHAW and ILLIAiM' FoNmLLnR, citizens of the United States, residing at Hackensack, in the coun- 5 ty of Bergen and-State of New Jersey, and at New York, in the county of New York and State of New York, respectively, have invented certain new and useful improvements in Loaded ielephone-Line Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to loaded telephone lines, and more particularly to loaded phantom line systems. its object is to provide a system suitable for long distance telephone and superimposed telegraph working which, notwithstanding the varying conditions to which such systems are subjected in practice, shall be free or nearly so from disturb- 0 ances due to the unbalancing of associated circuits and conductors. I In long distance telephony it is a desirable practice to divide the line between distant stations into two or more sections and to provide at each point of division an amplifying system preferably comprising two amplifiers, one for repeating in each direction. To render such a sectional line suitable for the amplifiers, an artificial line or D balancing network, as it is sometimes called, is connected to the terminus of each section at each such point, the purpose of the artificial line being to neutralize the section to which it is joined to currents tend- 3. ing to cause singing of the amplifying apparatus. The artificial. line itself is maintained constant as to its electrical characteristics since it is not subject to outside dis turbances. coils in the external line sections has been unsatisfactory in such systems because transient changes in the characteristics of the loading coils in these sections is not or cannot be offset by corresponding changes in the artificial line sections without frequent ad justment of the artificial line.

Owing to the exposure of the line conductors to lightning or other source of strong foreign currents, the loading coils were subject to considerable changes in inductance to telephonic currents, resulting in singing of the repeaters. Another difiiculty arose from transient changes in the resistance of the The introduction of loading loading coils when telegraph currents were superposed upon the telephone currents, this resulting in serious impairment to telephonic transmission. It has been found that the changes in inductance referred to are caused by excessive residual magnetism in the cores of the loading coils, which varies from time to time and variably reduces or changes the winding inductances to very small magnetizing forces, such as those produced by telephonic currents. The result in general is a continual variation or irregularity which has imposed a serious limitation in the application of amplifying repeaters and telegraph instruments to loaded lines. For successful repeater or simultaneous telegraph working, it is necessary to maintain constant or nearly constant line characteristics.

The diflicult-ies referred to have been successfully overcome, in accordance with this invention, by introducing into the external line sections loading coils having cores of high magnetic permeability but constructed to present an interrupted magnetic circuit, whereby permanent changes in the magnetic characteristics of the core and consequent changes in the inductance of the loading coils are avoided and balance is maintained substantially constant between the external line section and the artificial line connected thereto, thus insuring fixed operating characteristics of the amplifying apparatus.

In a phantom system for telephone lines embodying this invention, the core of the phantom circuit loading coil, and preferably also of the side circuit loading coil, may be provided with a plurality of air-gaps uniformly distributed about the core. AL

though there is a slight increase in the ohmic resistance of the winding conductors, due to the air-gaps, there is, to odset this, a diminution of the effective resistance due to a reduction in hysteresis and eddy current losses in the core. More than this, the air-gap coils constructed in accordance with this invention give a very large'net gain in line efficiency by permitting the use of repeaters adjusted to a very high degree of amplification, and by permitting more satisfao.

tory telephonic transmission under the condition of superposed telegraph working.

The air-gaps introduced unto the core of the phantom coil, may separate the core into four quarter sections, corresponding to the four winding sections, although it is within the scope of this invention to employ a larger number'than four or less than four, say two, likewise uniformly distributed arou the core. Even one gap may sometimes be employed if specially positioned with respectto the coil windings. Two air-gaps have actually been found suflicient and preferable under certain conditions for the phantom coil, and are also the preferred number. Under'all conditions, however, it is important that the gaps shall be symmetrically located with respect to the plurality of windings which go to make up the line wmdings of the coil.

'The single figure of the drawing illustrates diagrammatically a phantom telephone line system embodying this invention.

Four line conductors 1, 2, 3, 4 are arranged to provide three circuits, one a side circuit of conductors 1 and 2 extending between telephone stations 5and 6; another also a side circuit of conductors 3 and 4 extending betweenstations 7 and 8, and a third or phantom circuit of conductors 1, 2 and 3, 4 extending between stations 9 and 10. v

The circuit of conductors 1, 2 is provided with side circuit loading coils 11 and 12, and an amplifying system comprising repeaters 13 and 14. The circuit of conductors 3 and 4 is likewise prbvided with side circuit loading coils 15 and 16, and an amplifying system comprising repeaters 17 and 18. The phantom circuit is provided with phantom .loading coils 19 and 20 and an amplifying system comprising repeaters 21 and 22. Each of the phantom loading coils, 19 for example, is provided-with a core 23, with a plurality of. air-gaps 24, and eight. windings, 26 to 33 inclusive distributed around the core in quarter sections or quad-. rants, with the outer winding, say 26, of one quadrant in series with the inner winding 32- of the opposite quadrant. The air-ga s 24 are ,.uniformly distributed around t e core; ,As shown, they may separate the core into four quadrants corresponding to thefour winding sections.

Each of the side circuit coils, for example 11, is provided with a core 34 having two diametrically opposite air-gaps 35 and 36.

- On this coil there are but four windings 37 to 40 inclusive, distributed as shown on the two half core sections, the outer winding of one-half section, say 37, being connected in series with the inner winding'etO of the other half section, the windings 38 and 39 bein similarly connected. Y

The principal function of the air-gaps,

when used in loading coils, is to insure that the electrlcal constants of the coil for telephone conditions will not be materially altered by any degree of magnetization that may be superposed on the core along with the small forces due-to the telephone currents themselves. The air-gaps impart to the magnetic circuit not only resistance to magnetization but also the property of selfdemagnetization, in consequence of which the removal of the residual magnetism is accomplished when the superposed magnetic force is withdrawn.

These effects, as pointed out in detail in application Serial No. 861,121, filed September 12, 1914, for apparatus for loaded telephone line systems, which matured into Pat out No. 1,289,941, Dec. 31. 1918, and of which this application is a division, depend on the proportion of the air-gaps to the iron circuit, and are greater as the length of the gap is increased. Since an increase in the demagnetization factor results also in a reduction of the effective permeability of the core, and consequently in an increase of the amount of copper necessary to give the same inductance as well as an increase in the size and cost of the iron case, the best length of the gaps will be that which just gives a sufficient demagnetizing effect to insure that under any conditions of superposed magnetization that may arise in practice, the electrical constants of the coil will not vary more than an amount known not to be harmful.

The proper proportions of the air-gap in each case are best determined directly by experiment. This may be done by observing for :various lengths of gap the total range of change of the effective permeability of" the whole magnetic circuit to the small "forces dueto telephone currents after the coil,has been subjected to various cycles of strong magnetization, such as may be met with in practice. The proper air-gap will be chosen from these observations as that for which the total variation does not exceed the limiting value, say,.5%, imposed by the working requirements of the telephone line. A similar method may be followed to determine the most suitable gap to use in cases where thevariation of the effective resistance of the coils is the limiting requirement, such as the ease of simultaneous use of the line conductors for telephoning and telegraphing.

The amplifying repeaters referred to may be of the audion type, each, for example 13, comprising a cathode in the form of a heated filament 4.6, an output electrode or late 47, and an input electrode or grid 48.

he filament is heated by a battery 49. A battery 50 is provided in the output circuit, which includes also the primary winding 51 of an output repeating coil. A battery 52 is included in the input circuit, which also includes the secondary Winding 53 of an input repeating coil. The secondary wind lugs 54 of the output repeating coil are included serially in a part of the circuit system of conductors l and 2, this part being electrically balanced at the amplifying apparatus by a line network 55. The primary windings Q6 of the input repeating coil are bridged across the other part of the circuit system of conductors 1, 2, and this other part is likewise balanced by a line network 57.

The repeater 13 is adapted to repeat telephonic currents transmitted from station 5 to station 6. In the same manner the repeater 1a is adapted to repeat from station 6 to 5. It will be noted that the phantom circuit, through the amplifying system including the audions 21, 22, is completed by way of conductors'58, 59, 60 and 61 tapped from the middle points of the windings 56 of the other two circuits.

Although only one set of amplifiers and two sets of loading coils are shown for each circuit, it is to be understood that a greater number of each may be and ordinarily would be used in practice.

lVhenever the loading coils are invaded by strong foreign currents, the demagnetizing poles, due to the plural air-gaps, may be relied upon to maintain the line characteristics practically constant and a practically perfect balance between the several parts of the circuits and their line networks. It is therefore possible in a system constructed in accordance with this invention to use very powerful repeaters adjusted to their maximum degree of amplification and to give satisfactory telephone service under the severest conditions of simultaneous telegraph working.

What is claimed is 1. A telephone line comprising loading coils and an amplifying device comprising an artificial line balancing said telephone line, each of said loading coils having a plurality of core sections .eparated by non-magnetic gaps.

2. A telephone line comprising loading coils and an amplifying device comprising an artificial line balancing said telephone line, each of said loading coils having a toroidal core with a plurality of nonmagnetic gaps.

3. A telephone line comprising loading coils and an amplifying device comprising an artificial line balancing said telephone line, each of said loading coils having a plurality of core sectionsof equal length separated by non-magnetic gaps.

4:. A telephone line, system comprising phantom and side circuits, and loading coils and amplifying devices in certain of saidcircuits, said amplifying devices comprising artificial lines balancing the corresponding line circuits, each of said loading coils having a toroidal core with a plurality oil nonmagnetic gaps.

comprising loading coils, with 5. The combination with a telephone line and an amplifier connected therewith, of an artificial line connected and cooperating with said amplifier to render the same neutral to currents tending to cause singing thereof, and loading coils for the telephone l1n e presenting an interrupted magnetic circuit. j

b. A telephone line comprising a plurality of sections, amplifiers for repeating between said sections, each line section including loading coils having discontiuous magnetic cores the self-demagnetizing force of which is suilicient to maintain substantially constant. the permeability of the cores to telephonic currents under varying degrees of residual magnetism, and a balancing artificial line connected to each telephone line section.

7. The combination with a telephone circuit and an amplifier therefor, of an artificial line adapted to render said amplifier neutral to currents tending to cause singing,

and loading coils in said telephone circuit provided with stabilizing means whereby a balance is maintained between said telephone circuit and said artificial line.

8. In combination, a telephone line subject to outside disturbances, a balancing artificial line not subject to said disturbances, a plurality of circuits connected in conjugate relation to said telephone line and balancing line, and loading coils in said telephone line, said loading coils being so constructed as to be substantially free from changes in inductance due to said outside disturbances.

9. The combination of a telephone line comprising loading coils, with a balancing line, and a plurality of circuits connected in conjugate relation to said telephone line and said balancing line, said telephone line and coils being subject to the passage of telephone currents and other currents, said balancing line being subject to the passage of substantially only telephone currents, said coils being so constructed as to be substantially free from changes 'in inductance.

10. The combination of a telephone line a balancing line, and a plurality of circuits connected in conJugate relation to said telephone line and said balancing line, said telephone lineand coils being subject to the passage of telephone currents and other currents, said balancing line bein subject to the passage of substantially on y telephone currents, said coils having cores forming, nearly complete magnetic circuits with relatively small gaps lltl ranged with respect to said core segments, a circuit operatively connected to said telephone circuit comprising separate paths for currents transmitted in said telephone circuit in opposite directions, and a circuit simulating the electrical characteristics of said telephone circuit so related to said paths as to prevent currents from one of said paths from flowing in the other of said paths.

12. In a telephone system, four line conductors forming two side circuits and a phantom circuit, a loading coil for said phantom circuit comprising a segmental core having magnetic gaps and windings in each of said conductors symmetrically arranged with respect to said core segments, a circuit operatively connected to said phantom circuit comprising separate paths for currents transmitted in said phantom circuit in opposite directions, and a circuit simulating the electrical characteristics of said phantom circuit so related to said paths as to prevent currents from one of said paths from flowing in the other of said paths.

In witness whereof we hereunto subscribe our names this ninth day of July, A. D. 1918.

THOMAS SHAW. WILLIAM FONDILLER. 

